An organic light emitting diode (OLED) is a current-mode light emitting device. Due to advantages such as spontaneous light emitting, fast response, wide-viewing angle and ability to be fabricated on a flexible substrate, the OLED is more frequently used in a field of high performance display. OLEDs can be classified into two kinds of passive matrix driving OLEDs (PMOLEDs) and active matrix driving OLEDs (AMOLEDs) based on driving modes thereof. With respect to traditional PMOLEDs, with increasing of size of a display apparatus, a driving time of a single pixel is usually required to be reduced, thus a transient current flowing through a PMOLED is required to be increased, and thereby power consumption will be increased significantly. In contrast, with respect to AMOLEDs, as a current is inputted into each AMOLED by progressive scanning of a thin film transistor (TFT) switching circuit, existing problems can be well solved.
In existing AMOLED products, in order to reduce cost for manufacturing a driving integrated circuit (IC), a demultiplexer (DEMUX) is usually formed on a glass substrate. In this way, in a data transmission, a data signal is separated into red, green and blue (RGB) signals through the DEMUX, and the red, green and blue signals are respectively transmitted to R, G and B data lines on a back plate, and are stored by capacitors on the R, G and B data lines, so that when a gate scanning signal is inputted, the RGB signals are transmitted into RGB pixel electrodes respectively.
Specifically, FIG. 1 shows a configuration of an AMOLED pixel driving circuit commonly used in current market, and FIG. 2 shows a timing diagram of driving signals of the pixel driving circuit. Operation principle of the pixel driving circuit is described briefly below. The pixel driving circuit operates in three stages, wherein a first stage is a reset stage, a second stage is a data write stage, and a third stage is a light emitting stage. As an example, all transistors in the pixel driving circuit are PMOS transistors. In the first stage, a reset signal Vref is an effective signal. When the reset signal Vref is an effective signal (that is, a signal of low level as shown in FIG. 2), a transistor M1 is turned on, thereby a connected node between a capacitor C and a gate of a transistor M6 is discharged to be reset. During a period after the reset signal Vref changing from the low level to a high level and before a scanning signal Gate being effective (being in low level), the DEMUX is activated. In this period, RGB signals are inputted into RGB data lines respectively through the DEMUX, and are stored by capacitors on the RGB data lines. In the second stage, the scanning signal Gate is effective, thus transistors M3 and M2 are turned on, and thereby the signals on the RGB data lines are inputted into a source of the transistor M6, then a signal Data+Vth is written into the gate of the transistor M6 through the transistor M6, wherein Vth is a threshold voltage of the transistor M6. In the third stage, an emission signal Em is effective (being in low level), thus the transistors M4 and M5 are turned on, meanwhile the signal Data+Vth on the gate of the transistor M6 is maintained by the capacitor C, so that the transistor M6 is always in turned-on state during the light emitting stage, and emitted light compensation is achieved. It can be seen that, using such a design with a DEMUX, signal time of the scanning signal is partially occupied to write the signal Vth into the gate of the transistor M6, thus time for writing the data signal is reduced, and charging time of a pixel is reduced, thereby charging rate of the pixel is reduced, and display quality of the AMOLED product is seriously affected.